Method of preparing sulphite pulp for filaments and films



Patented Sept. 8, 1931 UNITED ST TES PATENT OFFICE CHARLES A. BLO IDGETT, OF SOUTH BREWER, AND HUGO H. HANSON, 0F BANGOR, MAINE,

ASSIGNORS TO EASTERN MANUFACTURING COMPANY, OE SOUTH BREWER, MAINE,

A CORPORATION OF MASSACHUSETTS METHOD OF PREPARING SULPHITE PULP FOR FILAMENTS AND FILMS No Drawing. Application filed April 26,

This invention relates primarily to a process for the production from woody products of a cellulose of high purity and other desirable characteristics in maximum quantity and especially suitable and receptive for the production therefrom of rayon or artificial filaments or fibres, irrespective of Whether. such filaments are obtained from a base of cuprammonium cellulose or xanthated cellulose, or whether said filaments consist of or comprise a cellulosic ester such as acetated cellulose or nitrated cellulose, or a cellulosic ether as an alkylor aryl-cellulose, typified by ethylated cellulose.

More specifically, this invention relates to the preparation and purification of wood pulp in such a manner and under such conditions that the amount of desirable or alphacellulose normally present in raw material is substantially conserved and the deleterious, components of the wood, sometimes generalized as incrusting bodies, are removed to the maximum, but with the minimum breaking down or altering. of the desirable form or forms of cellulose contained therein for the purposes comprehended in this specification and set forth in the accompanying claims.

Based upon the usual methods of production, wood pulps are broadly classified into mechanical pulps, which are produced primarily by methods involving attrition, and chemical pulps wherein the subdivision and purification of the original form of cellulose is primarily dependent upon chemical treatment, or chemical treatment aided by solvent action, and it is with this latter class of products that this invention is primarily concerned.

Raw wood may be first reduced mechanically to the form of chips of the desired sizes, which are then mixed with a sulphite liquor of the desired concentration, containing from O.5%-0.65% of SO combined as calcium acid sulphite, or O.35%0.45% of SO, combined as magnesium acid sulphite, together With about 3%5% of sulfur dioxide in the form of sulfurous acid, and in the initial proportion of 1 part of wood to about 5 parts of liquor, the cellulose being calculated as in 1927. Serial No. 186,810.

the air dry condition. The mass is then heated, with or without agitation, to 3, final condition represented by pounds to 7 0 pounds pressure per square inch above atmosphere, and about or a little above 290 F. until the degree of conversion desired has taken place. The resultant mass, so-called raw cooked pulp is then washed and usually screened and treated by ways now known, when it is,

ready for the second treatment.

In this, the apparatus employed may consist of the usual form of rotary boiler employedvin boiling rags, in which container the pulp is charged still containing moisture, and in the proportion of 1 part air dry pulp to 4 parts of water, more or less, the water containing dissolved therein sodium sulphite, sodium hydroxide and sodium sulphide. The ratio of sodium hydroxide, sodium sulphide and sodium sulphite may vary between the amount of 1 of the alkali (hydroxide and sulphide) components to to 2 of the sulphite, depending upon the resistance of the pulp to treatment and the use or uses to which it is intended the purified cellulose obtained therefrom shall be put.

The proportions of reactants to be em ployed under the conditions of treatment carried out will vary, depending upon the nature of the original cellulose operated upon, its composition, the length of time and other factors of the previous treatment to which the cellulose was subjected, and to the particular purpose for which the finished cellulose is to be used, as will be readily understood by those conversant with this art.

The liquior ratio of air dry cellulose will vary usually within the limits of 1 part of air dry cellulose to 4 parts of liquor, and l part of air dry cellulose to 7 parts of liquor, the cook being brought up in temperature as rapidly as possible to 280 F. and held there for between 2 and 3 hours.

A final product of 95% alpha-cellulose or better may be obtained for example, by operating upon a partially bleached wood pulp, and treating the same as herebefore outlined with a composition of 4%6% sodium hydroxide, 4:%6% sodium sulfide and 7%-9% sodium sulphite; the time and temperature of heating bein of the same order as before, and being modified according to the condition and extent of bleaching of the wood pulp employed and the uses to which the finished product is destined.

If desired, the pulp may be subjected to a final partial bleaching treatment by ways now known.

The final product is a cellulose of unusually high alpha-cellulose content, characterized by great strength of fibre, relative freedom from association with other cellulosic products inimical for the purposes intended, and on account of these desirable properties, esters and ethers of cellulose prepared therefrom give greater and more ready solubility, and films produced therefrom possess great strength, tenuity, extensibility and resistance, and therefore are especially suitable for rayon and filament formation, and the conversion into cellulose esters, ethers and other compounds and derivatives.

Moreover, as a result of the treatment herein described the physical condition of the pulp is altered in that the slime or gel forming constituents on the surface of the fibres have been dissolved off, leaving the fibres more pliable and of better felting ability but with less tendency to adhere firmly to one another. (The slime or gel acting as an agglutinant). As a result of this change if a quantity of the initial pulp and a quantity of the final product be prepared for making into hand-sheets of paper, as for example, by being beaten in a ball mill (for approximately 50 minutes) and then hand-sheets be made by the usual methods, having the same weight per unit of area, it will be found that the sheets made from the pulp produced by the herein described process will have a tearing strength 20-66% greater and a bursting strength 3040% less than the sheets made from the initial pulp. It is possible, however, to increase the gel forming constituents of this pulp so that the comparison herein shown with ordinary pulp will be modified, e. g. if the pulp prepared by this process is beaten as in a ball mill for a much longer time, for example three to four hours.

In the etherification of cellulose where the product may be projected through minute orifices and filaments made therefrom, it has been found, in the employment of the cellulose as prepared by means of this invention, that in the manufacture of ethyla-ted cellulose, the preliminary step of alkali-cellulose formation may be carried out more uniformly and with less fouling of the caustic sodasolution used, and less ethyl sulfate employed for alkylation. Furthermore, the alkyl-cellulose thus produced is unusually stable and may be prepared of great range of solubility in relatively inexpensive solvents, and solvent combinations. Filaments produced therefrom are of high physical strength and other desirable properties.

In the manufacture of rayon products and artificial filaments by the above methods of silk substitute formation, uniformly satisfactory results are to be obtained by the employment of a purified wood cellulose as prepared according to this invention, and of a purity, tensile strength, elasticity and other desirable properties to a degree hitherto unattainable.

In this specification where statements of percentages of alpha-cellulose are given, it is to be understood that the percentages are those obtainable by the methods of alkali hydroxide solubility determinations as found in textbooks and works of reference on cellulose technology.

In certain aspects, the present invention includes improvements in the methods and products described in our copending applications:Serial No. 87,806; filed February 12, 1926 ;--Serial No. 113,551, filed June 3, 1926; and Serial No. 127,700, filed August 6, 1926.

We claim:

1. A process for the treatment of cellulosic material for rayon manufacture comprising heating wood for several hours at temperatures progressively rising, up to about 290 F. under pressure of 60-70 pounds per square inch, in a closed container with a sulphite liquor containing free sulfur dioxide, in the initial proportion of 1 part air dry wood to about 5 parts liquor until the degree of action desired has taken place, then washing the cellulosic mass, and boiling the product thus obtained in a suitable container with agitation in an aqueous solution containing sodium hydroxide, sodium sulfide and sodium sulphite, at elevated temperature and pressure, washing the cellulose thus obtained free from soluble matters, and removing water therefrom.

2. A process for the treatment of cellulosic material for filament manufacture comprising heating celluosic material under pressure in a closed container for several hours with an alkali earth metal bi-sulphite with free sulfurous acid in the initial proportion of 1 part air dry cellulosic material to about 5 parts liquor, then washing the cellulosic mass free from reactants, and heating the product thus obtained in a rotary boiler in an aqueous solution containing sodium hydrox1de, sodium sulfide and sodium sulphite in the ratio of 1 of the alkali (hydroxide and sulfide) component, to 2 of the sulphite at 280 F. for 24 hours, washing the cellulose thus obtained free from soluble matters and removing water therefrom.

3. A process for the treatment of cellulosic material for alpha-cellulose manufacture comprising heating up to about 290 F. cellulosic material in a closed container for several hours with a sulphite liquor containing 5.5% free and combined sulfur dioxide, in the proportion of one part air dry cellulose to period of around three hours, at about 45 about 5 parts liquor, until the degree of aclb. gauge pressure, removing the contents of tion desired has taken place, then washing the boiler therefrom, and washlng.

the cellulosic matter free from reactants and Signed by us at So. Brewer, Maine, this cooking the product thus obtained in a ro- 23rd day of April, 1927.

tary boiler with agitation, in an aqueous solution of sodium hydroxide, sodium sulfide and sodium sulphite in the ratio of 1 of the alkali (hydroxide and sulfide) component to -2 of the sulphite at elevated temperature and pressure, washing the cellulose thus obtained free from soluble matters, and removing water therefrom.

4. A process for the treatment of cellulosic material obtained from wood especially adapted for viscose, cuprammonium and denitrated nitrocellulose rayon filament manufacture and for the production of cellulose ethers and cellulosic inorganicand organic esters, comprising heating the raw cellulosecontaining material after mechanical reduction in size of pieces or particles, to treatment with a sulphite liquor of the desired concentration and containing O.8%-1.2%

combined as metallic sulphite with about 3.0%5.0% SO; in the form of sulfurous acid. and in the proportion of 1 part of wood to about 5 parts of liquor, heating the mass preferably with agitation to a final temperature represented by about pounds per square inch and 290 F., until the degree of conversion desired has taken place, removing reactants from the resulting mass and then placing the mass in a rotary boiler with dissolved reagents in the proportion of about 1 part air dry pulp to 4 parts of water, the latter containing 5%-7% of a mixture of sodium hydroxide and sodium sulfide, together with an approximately equal amount of sodium sulphite, as rapidly as possible bringing the cook up to a temperature of 280 F., holding it there for a period of around three hours at about 45 lb. gauge pressure, after which the contents of the boiler are removed therefrom, and the said contents washed.

5. A process for the treatment of sulphite wood pulp comprising heating'said pulp in a rotary boiler with agitation, in an aqueous solution of sodium hydroxide, sodium sulfide and sodium sulphite inthe ratio of 1 of the alkali (hydroxide and sulfide) component to F 2 of the sulphite at elevated-temperature and pressure, washing the cellulose thus obtained free from soluble matters, and removing water therefrom.

6. A process for the treatment of sulphite wood pulp comprising heating said pulp in a rotary boiler with dissolved reagents in the proportion of about 1 part air dry pulp to 4 parts of water, the latter containing 5%7% of a mixture of sodium hydroxide and sodium sulfide, together with an approximately equal amount of sodium sulphite, as rapidly as possible bringingthe cook up to a temperature of 280 F., holding it there for a CHARLES A. BLODGETT. HUGO H. HANSON. 

